Hybrid Sol–Gel Glasses with Glass‐Transition Temperatures Below Room Temperature

Abstract

Melting gels are hybrid gels that have the ability to soften and flow at around 100°C for some combinations of mono-and di-substituted alkoxysiloxanes, where substitutions are either all aromatic or all aliphatic. In this study, melting gels were prepared using phenyltriethoxysilane (PhTES) and dimethyldiethoxysilane (DMDES), meaning both an aromatic and aliphatic substitution. Differential scanning calorimetry was performed to identify glass-transition temperatures, and thermal gravimetric analysis coupled with differential thermal analysis (TGA-DTA) was performed to measure weight loss. The glass-transition temperatures (T g ) ranged from -61°C to +5.6°C, which are between the values in the methyl only system, where all T g values are less than 0°C, and those values in the phenyl only system, where T g values are greater than 0°C. The T g decreased with an increase in the DMDES fraction. Below 450°C, the gels lost little weight, but around 600°C there was a drop in weight. This temperature is lower than the temperature for gels prepared with only aromatic substitutions, but higher than that for gels prepared with only aliphatic substitutions. Final heat treatment was carried out at 150°C for the gel with 80%PhTES-20%DMDES (in mol%), and the consolidation temperature increased with increasing DMDES content to 205°C for the gel with 50%PhTES-50%DMDES. After this heat treatment, the melting gels no longer soften.

Platinum free thermally curable siloxanes for optoelectronic application – synthesis and properties

“…This argument is supported by the detected D 1 However in these studies TAS is condensed rst for several hours before DAS is added dropwise. 26,[34][35][36][37] This leads to highly cross-linked structures, mainly consisting of regions with full condensed T 3 -T 3 units with D 2 , T 2 and D 1 groups connecting the edges of this regions. 38 In our studies the addition of DAS directly to the condensation reaction of TAS units leads to a less cross-linked and exible structure with T 1 , T 2 and T 3 units.…”

29Si NMR and SAXS investigation of the hybrid organic–inorganic glasses obtained by consolidation of the melting gels

“…In addition, Raman bands placed at 1413 cm −1 , 1223 cm −1 and 743 cm −1 were assigned to δ asym CH 3, δ sym CH 3 and ρ CH 3 , respectively 55 . The high intensity of the peaks assigned to the organic groups can be credited to the presence of the methyl groups to the surface of the hybrid glasses investigated 4,5,12 . Moreover, in the Raman spectra of the both samples, we also identified a very weak peak at 864 cm −1 which was assigned to the δ Si-O-C.…”

“…Melting gels are hybrid organic inorganic materials in which the presence of the covalent bonds between the organic components and inorganic network places the melting gels in the Class II of hybrids 2 . The precursors used for preparation of hybrid melting gels are a mixture between a mono-substituted organo-modified alkoxide such as phenyltriethoxysilane 3,4 or methyltriethoxysilane 5 and a di-substituted organo-modified alkoxide such as diphenyldiethoxysilane 3 or dimethyldiethoxysilane 5 . Hybrid melting gels differ from classical hybrids through their properties.…”

“…The consolidation temperature T 2 corresponds to cross-linking of the silica chains 5,6 . At the consolidation temperature the melting gels are transformed into hybrid glasses 4 .…”

“…Using 29 Si MAS NMR and FT-IR spectroscopy, they identified the phenomena that take place during the thermal transition from melting gels to hybrid glasses. Using the same system 3 and phenyltriethoxysilane along with dimethyldiethoxysilane 4 we characterized the structure of the hybrid glasses by Raman and FT-IR spectroscopy. The structure and the orientation of the organic groups was found to promote hydrophobicity to the surface of the hybrid glasses.…”